The following abbreviations are utilized throughout this document:    3GPP Third Generation Partnership Project    ALG Application Layer Gateway    APN Access Point Name    CPE Customer Premises Equipment    CSG Closed Subscription Groups    DHCP Dynamic Host Configuration Protocol    DNS Domain Name Server    DSL Digital Subscriber Line    EBI EPS Bearer ID    ECGI E-UTRAN Cell Global Identity    eNB evolved Node B    EPC Evolved Packet Core    EPS Evolved Packet System    E-UTRAN Evolved Universal Terrestrial Radio Access Network    femtoBS femto Base Station    FMC Fixed Mobile Convergence    FTTH Fiber to the Home    GERAN GSM/Edge Radio Access Network    GGSN Gateway GPRS Support Node    GRE Generic Routing Encapsulation    GTP GPRS Tunneling Protocol    GW Gateway    HNB Home Node B    HeNB Home Evolved Node B    IP Internet Protocol    IMSI International Mobile Station Identifier    ISP Internet Service Provider    ISR Idle State signaling Reduction    LBO Local Breakout    LIPA Local IP Access    LTE Long Term Evolution    MME Mobility Management Entity    MSC Mobile Switching Center    NAS Non Access Stratum    NAT Network Address Translation/Translator    OMA DM Open Mobile Alliance Device Management    PCC Policy and Charging Control    PDN Packet Data Network    PGW PDN Gateway    PMIP Proxy Mobile IP    PON Passive Optical Network    RAT Radio Access Technology    RBS Radio Base Station    RRC Radio Resource Control    SAE System Architecture Evolution    SEGW Security Gateway    SGSN Serving GPRS Support Node    SGW Serving Gateway    SIPTO Selected IP Traffic Offload    TAI Tracking Area Identity    TAU Tracking Area Update    TEID Tunnel Endpoint Identifier    UE User Equipment    UMTS Universal Mobile Telecommunication System    UTRAN Universal Terrestrial Radio Access Network
The Third Generation Partnership Project (3GPP) is currently standardizing a concept referred to as a home base station. A residential subscriber may subscribe to a fixed access solution such as DSL. A mobile operator may then sell the subscriber a home base station, also referred to interchangeably as a femto base station (femto BS), which the subscriber attaches at home to his residential fixed access gateway.
The home base station connects to the operator's network via a secure tunnel (supposedly IPsec protected) to a security gateway (SEGW) at the border of the operator's network. Via the SEGW the home base station has connectivity with core network nodes such as a Mobility Management Entity (MME) and a Serving Gateway (SGW) using the S1 interface in the Evolved Packet System (EPS). Also, an optional HeNB GW may be used. In the 3G Universal Mobile Telecommunication System (UMTS), the home base station connect to the HNB GW via the SEGW, which has connectivity with the Serving GPRS Support Node (SGSN) and Mobile Switching Center (MSC) via the Iu interface.
A problem with the home RBS solution is that the standard for Local IP Access (LIPA) has not yet been finalized. LIPA provides for connecting the UE directly to local devices (i.e., devices in the residential network). Additionally, it is possible to access the Internet directly through the fixed DSL network utilizing Selected IP Traffic Offload (SIPTO). The reason for the second capability is to offload Internet traffic from the mobile operator's network and thus lower cost (in a flat charging model best effort Internet traffic would not increase the mobile operator's revenue). A good technical solution would allow simultaneous access to the Evolved Packet Core (EPC), local devices, and the Internet via the Internet Service Provider (ISP).
Another related problem is how to provide remote access to the local devices for a closed group of customers. This problem arises in a large number of use cases when there are many IP-enabled home appliances.
In one solution described in U.S. Patent Application No. 61/101,726 entitled, “Local Breakout in Home (e)Node B” by Telefonaktiebolaget LM Ericsson, a novel femtoBS function snoops the destination address in the IP headers of uplink packets from the UE, identifies locally destined packets, and forwards the locally destined packets to the local CPE network instead of into the IPsec tunnel towards the 3GPP network. This solution has the advantage that it does not impact the UE, which can use the same address and PDN connection as assigned by the 3GPP operator. However the solution requires non-trivial mechanisms to identify the traffic to be broken out locally, and does not address the possible situation in which the 3GPP operator assigns private addresses to the UE that may overlap with the address range used in the residential network. Such an overlap cannot be excluded, and setting up the address translation rules for such a scenario may be quite complex. In addition, Network Address Translation (NAT) also requires an Application Layer Gateway (ALG) in order to run specific applications in the local network, and also the user/UE is not able to indicate on a case by case basis whether it wants a certain Internet session/traffic flow to be routed directly via the broadband access network or via the 3GPP core network.
Another solution for the home RBS problem is described in U.S. Patent Application No. 61/101,797 entitled, “Local Breakout in HeNB with UE and HeNB Support” by Telefonaktiebolaget LM Ericsson. This solution is based on explicit signaling between the UE and the femtoBS to establish a separate bearer for LBO traffic. Two embodiments of the solution are described. A first embodiment integrates the signaling for local bearer establishment into RRC signaling, while the second embodiment integrates this signaling into NAS signaling (where the femtoBS snoops the NAS signaling message and infers the intention for local bearer establishment by UE). A disadvantage of the first embodiment is that it requires specific UE functionality and standardization, while a disadvantage of the second embodiment is that snooping of encrypted NAS messages is not possible.
Neither solution above offers the capability to remotely access the residential network.
A recent Qualcomm proposal in 3GPP proposed a solution for local access with a “Local” Serving GW and a PDN GW in the HeNB including signaling to the MME and a new interface to the GWs in the HeNB. This solution, however, has problems relating to the Serving GW placement in the femtoBS. First, this would violate the current SAE architecture assumption wherein currently there is only a single SGW assigned for the UE. Assigning a second SGW would affect all the mobility procedures due to the need to set up and release the additional SGW. Impacting all of the connected and idle mode mobility procedures has significant disadvantages. Second, if the Serving GW is placed in the femtoBS, many more S11 interfaces will be required between the MME and local Serving GWs. Finally, since the Serving GW is a common node for a UE moving between E-UTRAN and UTRAN/GERAN access, the Serving GW in the femtoBS would be required to have an interface to the SGSN and the RNC in case of a direct tunnel as well. Such a direct interface between the home node and the SGSN/RNC in the operator's network may be problematic to deploy.
Another variant has been proposed by Vodafone in “Local Breakout and Home (e)NodeB,” 3GPP SA WG2 temporary document S2-092301, and by Nortel in temporary document S2-092355. This proposal collocates the SGW and PDN Gateway with the HeNB, but provides only a single SGW for the UE. The SGW is relocated each time the UE moves to the home cell. This solution avoids the architecture impacts related to having two SGWs, but raises several other problems. For example, moving in and out of femto cells would be visible to the PDN GW, which would require extra signaling. In the roaming case, for instance, the home network would see signaling each time the UE moves in or out of the home cell. This problem is especially bad in the open access or campus scenarios.
The Vodafone/Nortel proposal also hinders Tracking Area Update (TAU) optimizations. With this solution, a Tracking Area Identity (TAI) list, which includes both the home cell and the surrounding macro cell, cannot be assigned to the UE since the proposal would require an SGW change and a TAU whenever the UE enters or leaves the home cell. The TAI list feature is quite important to reduce TAU signaling, especially in this scenario. Additionally, Idle State signaling Reduction (ISR) cannot be used with this solution. 3GPP has defined the complex ISR feature to reduce TAU signaling, and a scenario of home LTE cell with 2G/3G macro coverage (or 3G home cell with LTE macro coverage) is one where ISR seems most usable. However, the Vodafone/Nortel proposal would render ISR unusable since ISR requires a common SOW for both the home cell and the macro cells of the other Radio Access Technology (RAT).
Another issue is that the UE does not know before moving into the home cell whether local IP connectivity will be used. There may be many users who do not use local IP connectivity for whom SOW relocation would be unnecessary. With the Vodafone/Nortel proposal, there is no way to know this before the UE starts a mobility procedure into the home cell, and thus if the user does not intend to use local IP connectivity, the procedure may be done unnecessarily.